Diaper rash is characterized by the following:

• Skin signs. Diaper rash is marked by red, tender-looking skin in the diaper region — buttocks, thighs and genitals.
• Changes in your baby's disposition. You may notice your baby seems more uncomfortable than usual, especially during diaper changes. A baby with a diaper rash often fusses or cries when the diaper area is washed or touched.

Diaper rash can be traced to a number of sources, including:

• Irritation from stool and urine. Prolonged exposure to urine or stool can irritate a baby's sensitive skin. Your baby may be more prone to diaper rash if he or she is experiencing frequent bowel movements or diarrhea because feces are more irritating than urine.
• Chafing or rubbing. Tightfitting diapers or clothing that rubs against the skin can lead to a rash.
• Irritation from a new product. Your baby's skin may react to baby wipes, a new brand of disposable diapers, or a detergent, bleach or fabric softener used to launder cloth diapers. Other substances that can add to the problem include ingredients found in some baby lotions, powders and oils.
• Bacterial or yeast (fungal) infection. What begins as a simple skin infection may spread to the surrounding region. The area covered by a diaper — buttocks, thighs and genitals — is especially vulnerable because it's warm and moist, making a perfect breeding ground for bacteria and yeast. These rashes can be found within the creases of the skin, and there may be red dots scattered around the creases.
• Introduction of new foods. As babies start to eat solid foods, the content of their stool changes. This increases the likelihood of diaper rash. Changes in your baby's diet can also increase the frequency of stools, which can lead to diaper rash. If your baby is breast-fed, he or she may develop diaper rash in response to something the mother has eaten.
• Sensitive skin. Babies with skin conditions, such as atopic dermatitis or seborrheic dermatitis (eczema), may be more likely to develop diaper rash. However, the irritated skin of atopic dermatitis and eczema primarily affects areas other than the diaper area.
• Use of antibiotics. Antibiotics kill bacteria — the good kinds as well as the bad. When a baby takes antibiotics, bacteria that keep yeast growth in check may be depleted, resulting in diaper rash due to yeast infection. Antibiotic use also increases the risk of diarrhea. Breast-fed babies whose mothers take antibiotics are also at increased risk of diaper rash.